The present invention relates generally to diagnostic imaging and, more particularly, to an integrated scintillator and collimator and method of manufacturing same.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
As stated above, typical x-ray detectors include a collimator for collimating x-ray beams such that collection of scattered x-rays is minimized. As such, the collimators operate to attenuate off-angle scattered x-rays from being detected by a scintillator cell. Reducing this scattering reduces noise in the signal and improves the final reconstructed image. Therefore, it is necessary that the scintillator array and the collimator, typically plates extending along one dimension above the scintillator array, are uniformly aligned. That is, exact mechanical alignment is required between the collimator plates and the cast reflector lines in the array of scintillators.
Known manufacturing processes attempt this exact alignment by constructing a continuous collimator that is sized to dimensionally match the width and length of the entire detector array. That is, the collimator plates are arranged or arrayed in a continuous consistent pattern or pitch that spans the entire detector length and is placed and attached to the detector rail structure. As such, individual scintillator arrays or packs are must then be exactly aligned to the continuous collimator to ensure that all scintillator cells and collimator cells are aligned exactly; otherwise the collimator must be discarded or repaired, or the scintillator packs must be discarded. This process requires excessively tight tolerancing and requires great operator skill and patience to assemble. Accordingly, these known processes are susceptible to waste of parts, material, and labor.
Additionally, as CT detectors grow in the z-direction, alignment requirements will tighten and the number of cells requiring alignment will increase. Therefore, the low process yields and high-end process scrap and re-work associated with these known manufacturing processes will increase the cost and time associated with CT detector assembly.
Notwithstanding the advances made in CT detector manufacturing, these known detector assemblies and assembly processes result in a detector with less than optimal collimation.
Referring to FIG. 10, a known CT detector 1 fabricated according to known manufacturing processes is shown. The CT detector 1 includes a series of tungsten collimator plates 2 that collimate x-rays projected toward scintillator cells 3 of a scintillator array 4. As shown, each of the collimator plates 2 is generally aligned with a reflector line 5 disposed between adjacent scintillators 3. The reflector lines 5 prevent light from being emitted between adjacent scintillators. The scintillator array is coupled to a photodiode array 6 that detects light emissions from the scintillator array and transmits corresponding electrical signals to a data acquisition system for signal processing. As readily shown, the collimator plates are not integrated with the individual scintillator elements 3. That is, an air gap 7 exists between the collimator plates and the scintillator cells 3. The air gap 7 typically results in a separation between the collimator plates and the scintillator array of approximately two to four thousands of an inch. This air gap occurs as a result of the manufacturing process whereupon the collimator plates are formed as a single collimator assembly that accepts and aligns an array of scintillators. The air gap, however, makes the CT detector susceptible to x-rays received between two collimator plates impinging upon an adjacent scintillator thereby resulting in undesirable anomalies in the final reconstructed CT image.
Therefore, it would be desirable to design an integrated scintillator and collimator absent the aforementioned air gap as well as a method of manufacturing such an integrated scintillator and collimator.